White House press secretary Sean Spicer holds up a document concerning a Washington Post story on Sally Yates as he talks to the media during the daily press briefing at the White House in Washington Tuesday, March 28, 2017. Spicer discussed the Supreme Court nominee Justice Neil Gorsuch, jobs, healthcare, and other topics. (AP Photo/Andrew Harnik)
White House press secretary Sean Spicer holds up a document concerning a Washington Post story on Sally Yates as he talks to the media during the daily press briefing at the White House in Washington Tuesday, March 28, 2017. Spicer discussed the Supreme Court nominee Justice Neil Gorsuch, jobs, healthcare, and other topics. (AP Photo/Andrew Harnik) Credit: Andrew Harnik

WASHINGTON — Potential White House entanglement in Congress’ investigation of Russian meddling in the 2016 election brought new protests from Democrats on Tuesday as fresh political allegations clouded the probe.

Devin Nunes, the chairman of the House intelligence committee which is conducting one of the congressional investigations, turned aside calls to step aside. Later in the day, the White House vehemently denied a report that it had sought to hobble the testimony of a former acting attorney general before Nunes canceled the hearing where she was to speak.

Nunes’ decision to cancel Tuesday’s hearing was the latest in a series of actions that Democrats contend demonstrate that his loyalty to Trump is greater than his commitment to leading an independent investigation. The California Republican, who was a member of Trump’s presidential transition team, has said he met with a secret source last week on White House grounds to review classified material that showed Trump associates’ communications had been captured in “incidental” surveillance of foreigners in late 2016.

Nunes would not name the source of the information, and his office said he did not intend to share it with other members of the committee. Nor would he disclose who invited him on the White House grounds for the meeting. He described the source as an intelligence official, not a White House official. In an interview on CNN, he suggested the president’s aides were unaware of the meeting.

Adding to the swirl of questions was the publication of a series of letters dated March 23 and March 24 involving a lawyer for former Acting Attorney General Sally Yates.

Yates, along with former CIA Director John Brennan and former director of national intelligence James Clapper, had agreed to testify publicly before the House intelligence committee. The canceled hearing would have been the first opportunity for the public to hear Yates’ account of her role in the firing of Trump’s first national security adviser, Michael Flynn.

The letters from lawyer David O’Neil, published by The Washington Post, appeared to be in response to a meeting O’Neil had at the Justice Department on March 23 in advance of the hearing. In them, O’Neil pushes back against what he says is Justice Department guidance on what Yates could say about conversations she had with Trump — conversations the department indicated could be covered by executive privilege.

Yates was fired in January as acting attorney general after she refused to defend the Trump administration’s first travel ban. She alerted the White House in January that Flynn had been misleading in his account of a December phone call with the Russian ambassador to the United States in which economic sanctions against Russia were discussed.